Lower esophageal sphincter pressure measurement is a widely used diagnostic test, and is presumed to be one important feature in preventing gastroesophageal reflux. However, the critical pressure determinants of this anti-reflux barrier are incompletely understood. Likewise, the key parameters of gastroesophageal reflux that lead to esophagitis are poorly defined. The purpose of these studies is to exploit modern computer technology in order to completely define both the normal and pathologic manometric features of the lower esophageal sphincter and to quantitate several aspects of acid reflux in both health and esophagitis. First a multivariant computer analysis of rapid versus station pull through techniques will be done. Next, the genesis of respiratory oscillations in sphincter pressure will be explored. Then, three dimensional aspects of the normal sphincter profile will be determined. The cause of the radial pressure asymetry will be investigated in man and the opossum. Finally, the key features of "normal" reflux (frequency, duration, mucosal hydrogen ion exposure, extent of mucosal involvement) will be assessed by computer, using a new multi-point pH recording device. In patients with reflux, the three dimensional pressure differences will be contrasted with normals. Then a comprehensive study of the quantitative aspects of esophageal acid reflux (frequency, duration, mucosal hydrogen ion exposure, extent of mucosal involvement) will be computer assessed. These studies will lead to a clearer understanding of the critical determinants of reflux esophagitis.